David S. Blehert, a microbiologist at NWHC, leads the laboratory study of this nefarious fungus. He enters the second dark room wearing Tyvek coveralls, rubber boots, latex gloves, a red-filtered headlamp, and a respirator. Moving quietly to avoid rousing the animals, he approaches a large glass-fronted cabinet in which sits a small, screened cage of bats. The cabinet is a florist's refrigerator, adopted by Blehert because hibernating bats, like cut lilies, do best at low temperatures and high humidity. Blehert peers into the cooler, checking the bats for evidence of fungal growth around their muzzles or on their wings. White fuzz on the snout, which looks like rime on the beard of a skier, is a signal that the bat may be infected; it's also the source of the label "white-nose syndrome" for this affliction.

No sign of change, Blehert tells me back in the locker room. No mortalities so far, and no visible fungus. But the experiment is still in an early stage.

How does this fungus kill the bats? "That we don't know," he says. "It is, I believe, the first disease ever characterized specifically targeting a hibernating animal." So its mode of lethality may be different from anything science has ever seen. And that's only one of the unknowns.

The fungus itself seems to be new to North America. Its presence was first documented—but not yet recognized—in a photograph taken in February 2006 at Howes Cave, west of Albany, New York. A year later, people began to report something peculiar: little brown bats flying outside nearby caves during daylight in the midst of winter. A little brown bat is a tiny creature, smaller than a human thumb, and dependent on its two grams of stored fat to keep it alive through the cold season. Hibernation is essential to making its energy resources last; a single arousal can cost it a month's worth of fat. When a crew from New York's Department of Environmental Conservation made their routine annual inspection of Hailes Cave, another hibernaculum nearby, they found thousands of dead bats, scattered all over the cave, in various stages of deliquescence and decay. "It was carnage," according to Al Hicks, a mammal specialist with the department.

Since then, the problem has spread quickly and far. Biologists estimate that a million or more animals were lost in three years, with populations at some sites eliminated. Six species have the disease, one of which had been declared endangered long before white-nose syndrome: the Indiana bat (Myotis sodalis). Three others are at very high risk, including the gray bat (Myotis grisescens), also endangered. Great progress was made within recent decades in restoring gray bat populations. "We've put enormous effort in this," says Merlin Tuttle, founder of Bat Conservation International. "It could now be unraveled in just a few years."